Excimer laser gas mixtures consist typically of 5 to 10% of a so-called active inert gas (e.g. krypton), 0.1 to 0.5% of a halogen donor such as F.sub.2 and a light buffer gas, such as helium or neon, at a total pressure of 1.5 to 4 bar. Said gas is brought between two elongated parallel electrodes and exposed to said high-voltage discharge. To produce laser pulses of high energy, in the high-voltage discharge between the electrodes very high current densities of typically 10.sup.3 A/cm.sup.2, power densities of 10.sup.6 W/cm.sup.3 and electron temperatures in the region of 1 eV are necessary. In commercially usable excimer lasers to achieve an adequate breakdown field strength the electrode spacing must be relatively small, typically in the region of 2 to 3 cm. The electrodes are therefore subjected to great stress by the adjacent plasma.
The life of excimer laser gases is limited mainly by two processes. Firstly, even in well passivated systems chemical dark reactions take place between the halogen and the container walls which lead to consumption of the halogen and to contaminations. Secondly, a slight electrode erosion during the high-voltage discharge also leads to chemical reactions. The products resulting from the electrode erosion may occur both in the form of particles and in the form of volatile metal fluoride compound. In the former case this leads to dust deposits on the inner walls of the laser chamber and this is particularly undesirable in the region of the mirrors and windows; in the latter case due to the laser radiation itself a metal film can deposit photochemically on the inner side of the windows, said film also being extremely detrimental.
The material of the laser electrodes is thus not only decisive to the life of the electrodes, the form of which varies with the electrode erosion, but also decisive for the life of the laser gas and the laser optical system.
Corresponding considerations apply as well to other pulsed gas lasers, such as N.sub.2 lasers or CO.sub.2 lasers.
The electrode material must therefore be carefully selected as regards its chemical and physical stability and strength. In the prior art electrodes are usually employed of nickel and in some cases also brass. Also known are aluminium electrodes with a nickel coating (see the article by H. Pummer, U. Sowada, P. Oesterlin, U. Rebhan and D. Basting in the journal "Laser und optoelektronik" Vol. 17 (2), p. 141-148 (1985)).
The invention is based on the problem of preparing an electrode for pulsed gas lasers, in particular excimer lasers, which have optimum properties as regards the above requirements. The electrode is thus to have a long life and avoid contaminations of the laser gas and of the optical components, such as mirrors and windows, of the laser.